One known type of inflator for a vehicle air bag system is shown in U.S. Pat. No. 4,698,107. The inflator comprises a cylindrical housing which encloses a solid gas generating material. In an emergency situation, the gas generating material is ignited, and generates inert, non-toxic gas (e.g., nitrogen), under pressure, within the housing. The cylindrical housing includes a series of nozzles which direct gas generated by the solid gas generating material out of the housing to inflate the vehicle air bag. As the gas is directed through the nozzles, thrust forces are applied to the cylindrical housing.
In many known inflator designs, the walls of the inflator housing are constructed of steel or other high strength metal. However, an inflator with a steel housing is relatively heavy. To reduce the weight of the inflator, it has been suggested to make the inflator housing of aluminum or other lightweight metal (see e.g., U.S. Pat. No. 4,561,675).
In the applicant's experience, inflator housings, whether made of steel or aluminum, normally have walls of substantially uniform thickness. That thickness is determined by the minimum thickness required in the areas of the walls containing the gas dispensing nozzles. The areas of the walls containing the gas dispensing nozzles tend to be the weakest structural areas of the housings, because the nozzles create discontinuities in the walls. Thus, it has been customary to construct the entire walls of the housings with a minimum thickness such that the portions of the walls containing the gas dispensing nozzles can withstand the gas pressures and thrust forces applied to the inflator housing during operation of the inflator.